The peripheral nervous system of vertebrates originates from two main cell classes: neural crest and cranial ectodermal placodes. Placodes are discrete regions of thickened epithelium that give rise to portions of the cranial sensory ganglia as well as form the paired sense organs (lens, nose, ears). Despite their importance to formation of the peripheral sensory nervous system in the head, comparatively little is known about the early development of the ectodermal placodes. The tools are now in hand to examine not only the basic developmental processes leading to placode development but also the molecular events underlying their formation. This knowledge is fundamental for understanding early development of the sensory organs/ganglia and to help identify and correct disorders in these essential structures. This proposal aims to characterize the cellular and molecular events underlying key events in development of placodes. Many of the experiments emphasize the olfactory placode since it is less well understood than many of the other placodes (e.g. otic, trigeminal). The olfactory placode arises within the anterior neural folds, which are the only region of the neuraxis that does not produce neural crest cells. We will assess the steps involved in competence, specification and commitment of the olfactory placode. We will explore whether and to what extent the olfactory placode has the capacity to form neural crest cells and vice versa by examining their ability to interchange for one another. Finally, we will examine the role of potential molecular regulators of placode formation/invagination and will functionally characterize selected novel molecular markers. Specific experiments will: 1) examine competence, specification and commitment of the olfactory placode. 2) examine whether olfactory placode can form neural crest and vice versa. 3) characterize the potential function of a novel chick spalt in placode development. 4) investigate the expression and function of Frzb-1 and an unknown gene, Placode-1 identified in a screen for placodal markers. [unreadable] [unreadable] [unreadable]